LI-RADS version 2018 for hepatocellular carcinoma < 1.0 cm on gadoxetate disodium–enhanced magnetic resonance imaging

Objectives We aimed to develop and evaluate a modified Liver Imaging Reporting and Data System (LI-RADS) version 2018 using significant ancillary features for diagnosing hepatocellular carcinoma (HCC) < 1.0 cm on gadoxetate disodium–enhanced magnetic resonance imaging (MRI). Methods Patients who underwent preoperative gadoxetate disodium–enhanced MRI for focal solid nodules < 2.0 cm within 1 month of MRI between January 2016 and December 2020 were retrospectively analyzed. Major and ancillary features were compared between HCCs of < 1.0 cm and 1.0–1.9 cm using the chi-square test. Significant ancillary features associated with HCC < 1.0 cm were determined by univariable and multivariable logistic regression analysis. The sensitivity and specificity of LR-5 were compared between LI-RADS v2018 and our modified LI-RADS (applying the significant ancillary feature) using generalized estimating equations. Results Of 796 included nodules, 248 were < 1.0 cm and 548 were 1.0–1.9 cm. HCC < 1.0 cm less frequently showed an enhancing capsule (7.1% vs. 31.1%, p < .001) and threshold growth (0% vs. 8.3%, p = .007) than HCC of 1.0−1.9 cm. Restricted diffusion was the only ancillary feature significant for diagnosing HCC < 1.0 cm (adjusted odds ratio = 11.50, p < .001). In the diagnosis of HCC, our modified LI-RADS using restricted diffusion had significantly higher sensitivity than LI-RADS v2018 (61.8% vs. 53.5%, p < .001), with similar specificity (97.3% vs. 97.8%, p = .157). Conclusion Restricted diffusion was the only significant independent ancillary feature for diagnosing HCC < 1.0 cm. Our modified LI-RADS using restricted diffusion can improve the sensitivity for HCC < 1.0 cm. Key Points • The imaging features of hepatocellular carcinoma (HCC) < 1.0 cm differed from those of HCC of 1.0–1.9 cm. • Restricted diffusion was the only significant independent ancillary feature for HCC < 1.0 cm. • Modified Liver Imaging Reporting and Data System (LI-RADS) with the addition of restricted diffusion can improve the sensitivity for HCC < 1.0 cm.